Evidence uncovered so far supports the theory that the two brothers suspected in the Boston Marathon bombings had no help, authorities said Saturday.

"From what I know right now, these two acted together and alone," Watertown Police Chief Edward Deveau told CNN. "I think we have to be ever vigilant, and we're learning as we go along, but as far as this little cell -- this little group -- I think we got our guys."

Deveau said investigators were continuing to look into where Tamerlan Tsarnaev, 26. and Dzhokar Tsarnaev, 19, may have gotten the resources to amass the cache of weapons used in the bombings and afterward. "We have to figure that out," he said. "There's a lot more work to go."

Photos: Nation mourns Boston bomb victims – People pause at the memorial site in Copley Square on April 30 in Boston. The city continues to return to normalcy with Boylston Street fully reopened and businesses back up and running after two weeks of closures. See all photography related to the Boston bombings.

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Nation mourns Boston bomb victims – Running shoes are among the mementos left as a tribute to the victims of the bombing.

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Nation mourns Boston bomb victims – Boston shows its resilience and heart with signs of support for the marathon bombing victims, including this cover from the new issue of Boston magazine.

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Nation mourns Boston bomb victims – Law enforcement officials enter St. Patrick's Church in formation prior to the funeral for Massachusetts Institute of Technology Police Officer Sean Collier in Stoneham, Massachusetts, on Tuesday, April 23. Collier was allegedly shot and killed by Boston Marathon bombing suspects Dzhokhar and Tamerlan Tsarnaev on Friday, April 19.

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Photos: Nation mourns Boston bomb victims – Members of many different law enforcement agencies walk in formation into Collier's funeral at St. Patrick's Church on April 23.

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Nation mourns Boston bomb victims – President Barack Obama observes a moment of silence in honor of the victims of the Boston Marathon bombings, in the Oval Office in Washington on Monday, April 22. Massachusetts Gov. Deval Patrick asked his state and beyond to honor the victims at 2:50 p.m., the time of the first explosion.

Nation mourns Boston bomb victims – Nurse practitioner Maureen Quaranto, who treated victims of the Boston Marathon bombings, wears her Boston Marathon jacket during Mass at the Cathedral of the Holy Cross on Sunday, April 21, in Boston.

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Nation mourns Boston bomb victims – From left, Boston Police Department Superintendents Kevin Buckley and William Evans attend the Mass at the Cathedral of the Holy Cross with Police Commissioner Edward Davis on April 21.

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Nation mourns Boston bomb victims – Photos of the deceased are displayed at the Cathedral of the Holy Cross on April 21, the first Sunday since the Boston Marathon bombings.

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Nation mourns Boston bomb victims – Boston Police Department Superintendent William Evans, right, kneels during the service at the Cathedral of the Holy Cross on April 21.

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Nation mourns Boston bomb victims – Parishioners gathered for a morning service at the Redeemer Fellowship Church on April 21, just a few blocks from the crime scene on Franklin Street where major police activity occurred on April 19 during the manhunt for Dzhokhar Tsarnaev, in Watertown, Massachusetts.

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Nation mourns Boston bomb victims – Leaders of an interfaith service participated in a vigil at the memorial for the victims of the Boston Marathon bombings, near the finish line on Boylston Street in Boston on April 21.

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Nation mourns Boston bomb victims – Crowds gathered to participate in an interfaith memorial service with leaders from six churches at a makeshift memorial for victims near the site of the Boston Marathon bombings at the intersection of Boylston and Berkeley streets on April 21.

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Nation mourns Boston bomb victims – The makeshift memorial honoring the victims of the Boston Marathon explosions on Boylston Street continues to grow as onlookers gather on April 21.

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Nation mourns Boston bomb victims – Nicole Collier Lynch, center, sister of slain MIT police officer Sean Collier, hugs a Wellesley police officer during a vigil at the Town Common in Wilmington, Massachusetts, on Saturday, April 20. Collier, 26, was shot multiple times in his car on Thursday night as Boston Marathon bombing suspects Dzhokhar Tsarnaev and his brother Tamerlan tried to evade capture.

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Nation mourns Boston bomb victims – A woman holds an American flag at a makeshift memorial on April 20, near the scene of the Boston Marathon explosions.

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Nation mourns Boston bomb victims – People gather at a makeshift memorial for victims on April 20.

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Nation mourns Boston bomb victimss – A flag decorates the memorial on Boylston Street in Boston on April 20.

Nation mourns Boston bomb victims – Items hang from a barrier Saturday at the makeshift memorial near the site of the Boston Marathon bombings.

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Nation mourns Boston bomb victims – Huntsville, Alabama, residents hold a prayer vigil on Friday, April 19, for those lost and injured in the bombing at the Boston Marathon. Three people died when two bombs went off Monday, April 15, near the finish line. View photos from the attacks.

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Nation mourns Boston bomb victims – A man rings a bell at the vigil in Huntsville on April 19.

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Nation mourns Boston bomb victims – Two women embrace during a candlelight vigil in Somerville, Massachusetts, for the victims of the Boston Marathon bombing on Thursday, April 18.

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Nation mourns Boston bomb victims – People hold candles as they listen to a speaker during a vigil in Somerville, Massachusetts, on April 18.

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Nation mourns Boston bomb victims – President Barack Obama talks with Massachusetts General Hospital staff on April 18 while visiting patients injured in the terror attack.

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Nation mourns Boston bomb victims – A man at the BoMA restaurant across the street from the Cathedral of the Holy Cross in Boston watches President Obama speak on television at the cathedral honoring the victims of the Boston Marathon bombings on April 18.

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Nation mourns Boston bomb victims – People watch President Obama at Cathedral High School in Boston on April 18.

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Nation mourns Boston bomb victims – A running shoe and U.S. flag are part of a memorial on the Boston Marathon route on April 18.

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Nation mourns Boston bomb victims – President Barack Obama and first lady Michelle Obama arrive at the interfaith service for the victims of the Boston Marathon bombing, at the Cathedral of the Holy Cross in Boston, on April 18.

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Nation mourns Boston bomb victims – Mourners filled the cathedral in Boston on April 18 for the the interfaith service.

Nation mourns Boston bomb victims – A flag flies at half staff on April 17 near the scene of the Boston Marathon bombings.

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Nation mourns Boston bomb victims – First lady Michelle Obama takes part in a moment of silence for victims of the bombings at the Boston Marathon during a bill-signing ceremony at the Maryland State House in Annapolis, Maryland, on April 17.

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Nation mourns Boston bomb victims – Flowers, running shoes and other items are left in memory of Chinese graduate student Lingzi Lu, who was killed during the bomb explosions on April 17.

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Nation mourns Boston bomb victims – Joy Liu, 23, puts a green hat with a shamrock and a note with the words "From Boston and Beijing with love. RIP" at the memorial for Lu.

Nation mourns Boston bomb victims – Brooks Orpik of the Pittsburgh Penguins shows his support for Boston with a sticker on his helmet during the Penguins' game against the Montreal Canadiens on April 17.

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Nation mourns Boston bomb victims – A moment of silence was held for the victims of the Boston Marathon bombings before a hockey game between the Boston Bruins and the Buffalo Sabres on April 17.

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Nation mourns Boston bomb victims – People pray during a vigil held by the city of Cambridge, Massachusetts, on April 17 to show support for those affected by the Boston Marathon bombings.

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Nation mourns Boston bomb victims – Dennis Seidenberg of the Boston Bruins observes a moment of silence for the victims of the Boston Marathon bombings before the start of an NHL hockey game in Boston against the Buffalo Sabres on Wednesday, April 17. It was the first sporting event held in the city since the bombings.

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Nation mourns Boston bomb victims – A man places a message for the victims of the Boston bombings at a memorial site in Boston on April 17.

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Nation mourns Boston bomb victims – Prior to an April 17 service at Marsh Chapel on the Boston University campus, members of the clergy walk past a memorial for graduate student Lu Lingzi, who was identified as the third person killed in the terror attack. Previously identified were Krystle Campbell, 29, of Arlington, Massachusetts, and Martin Richard, 8, of Dorchester, Massachusetts.

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Nation mourns Boston bomb victims – Danielle Cerroni writes a chalk message on the street on April 17 at the scene of the explosions near the finish line of the Boston Marathon.

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Nation mourns Boston bomb victims – Homeland Security Secretary Janet Napolitano observes a moment of silence for victims of the Boston bombing during a hearing before the Senate Homeland Security and Governmental Affairs Committee on April 17.

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Nation mourns Boston bomb victims – A woman looks at memorials left at the scene of the Boston Marathon explosions.

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Nation mourns Boston bomb victims – A man and woman leave after visiting the makeshift memorial on Boylston Street on April 17.

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Nation mourns Boston bomb victims – A mother and daughter hold one another during a vigil in memory of 8-year-old Martin Richard of Dorchester at Garvey Park in Boston on Tuesday, April 16.

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Nation mourns Boston bomb victims – A crowd holding candles gathers during a vigil on April 16 at Garvey Park in Boston for 8-year-old Martin Richard of Dorchester, who was killed in the marathon bombing.

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Nation mourns Boston bomb victims – People gather in Boston Common on April 16 for a candlelight vigil for victims of the bombings in Boston.

Nation mourns Boston bomb victims – Emerson College students embrace one another at the vigil on Boston Common on April 16.

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Nation mourns Boston bomb victims – Attendees hold candles in honor of the victims at an interfaith service at Arlington Street Church in Boston on April 16.

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Nation mourns Boston bomb victims – A woman uses her hand to keep wind from her candle as she stands with others around the pond in the Boston Public Gardens after a candlelight interfaith service at Arlington Street Church on April 16.

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Nation mourns Boston bomb victims – Mourners gather on the edge of the pond in the Boston Public Gardens for a candlelight vigil on April 16.

Nation mourns Boston bomb victims – Students from the Clifden Academy hold an American flag and candles during a vigil on April 16 in Dorcester, Massachusetts, in honor of 8-year-old Martin Richard, who was killed in the bombings.

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Photos: Nation mourns Boston bomb victims – People walk along the barricade at Boylston Street on April 16, following yesterday's bomb attack on the Boston Marathon.

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Photos: Nation mourns Boston bomb victims – On the shared porch of their home in Medford, Massachusetts, on April 16, Colleen Howe, left, and Lisa O'Leary grieve for their neighbor, Patty Campbell, who lost her daughter Krystle Campbell in the bombings.

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Photos: Nation mourns Boston bomb victims – Nicole Rand, left, who ran the marathon, embraces with her mother, Maureen Joham, on April 16 as she recounts her experience in Boston.

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Photos: Nation mourns Boston bomb victims – Attendees of the vigil sign a large poster in honor of the victims of the bombing on April 16.

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Photos: Nation mourns Boston bomb victims – Mourners hug one another during a vigil for victims of the Boston Marathon bombings at Boston Common

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Photos: Nation mourns Boston bomb victims – A man carries balloons, flowers and flags to a memorial for victims on April 16, just blocks from the scene of the bombings.

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Nation mourns Boston bomb victims – American flags hang from a barrier on April 16 at a roadblock staffed by National Guard soldiers at the end of Boylston Street near the site of the bombings in Boston.

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Nation mourns Boston bomb victims – Mike Vitale, who lives in the Boston area, prays beside a makeshift memorial at a roadblock at the end of Boylston Street.

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Nation mourns Boston bomb victims – Emerson College students Rachel Ferullo, left, and Kathryn Waxman at a vigil on Boston Common for victims of the bombings.

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Nation mourns Boston bomb victims – Runners Judy Adler, left, and her daughter, Rachel Schapiro, embrace during a moment of silence at the Baptist Health South Florida Brickell Run Club event organized on April 16 in Miami in honor of victims of the Boston Marathon bombings.

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Nation mourns Boston bomb victims – Five-time Boston Marathon runner Jose Sotolongo, center, reacts during a moment of silence at the Baptist Health South Florida Brickell Run Club event in Miami on April 16.

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Nation mourns Boston bomb victims – The New York Islanders and Florida Panthers stand for a moment of silence for the bombings at the Boston Marathon before their game at Nassau Veterans Memorial Coliseum on April 16 in Uniondale, New York.

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Nation mourns Boston bomb victims – Members of the Boston Red Sox observe a moment of silence before their game against the Cleveland Indians on April 16 in Cleveland.

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Nation mourns Boston bomb victims – People walk Boylston Street where memorials have been set up to the corner of Berkeley after the barricades were moved back on April 16.

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Nation mourns Boston bomb victims – A woman prays at a security gate near the scene of the bomb attack where visitors have congregated on April 16. See the aftermath in Boston.

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Nation mourns Boston bomb victims – From left, Boston Marathon runners Tammy Snyder, Diane Deigmann and Lisa Kresky-Griffin embrace at the barricaded entrance to Boylston Street near the finish line of the Boston Marathon on April 16.

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Nation mourns Boston bomb victims – Two young girls leave flowers on the steps outside the home of 8-year-old Martin Richards, who was killed in one of the explosions at the marathon.

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Nation mourns Boston bomb victims – Several former Heisman Trophy winners, including former Saints running back George Rogers, right, observe a moment of silence for the bombing victims Tuesday before working on a Habitat for Humanity home in New Orleans.

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Nation mourns Boston bomb victims – Traders observe a moment of silence on Tuesday before the opening bell on the floor of the New York Stock Exchange.

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Photos: Nation mourns Boston Marathon tragedy – The flag above the White House flies at half staff on Tuesday, April 16 in Washington.

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Nation mourns Boston Marathon tragedy – The Minnesota Twins stand during the national anthem before their game on Monday, April 15, in Minneapolis, following a moment of silence to honor the victims of the Boston Marathon bombings.

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Nation mourns Boston Marathon tragedy – President Barack Obama makes a statement about the bombings in the White House briefing room on Monday.

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Nation mourns Boston Marathon tragedy – Players and fans observe a moment of silence before the San Antonio Spurs and Golden State Warriors NBA game in Oakland, California, on Monday.

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Nation mourns Boston Marathon tragedy – A U.S. flag flies at half staff at the Capitol on Monday after House Speaker John Boehner ordered flags to be lowered.

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Nation mourns Boston Marathon tragedy – Fans pause for a moment of silence before the NHL game between the Phoenix Coyotes and the San Jose Sharks on Monday in Glendale, Arizona. See the world reaction to the attack.

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Photos: Nation mourns Boston bomb victims – Mark Trumbo of the Los Angeles Angels of Anaheim stands during the National Anthem following a moment of silence to honor the victims of the Boston Marathon bombing before the game against the Minnesota Twins on April 15, 2013 in Minneapolis, Minnesota. See all photography related to the Boston bombings.

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EXPAND GALLERY

Just Watched

Final moments of Boston terror manhunt

Manhunt for Boston bombers – Boston bombing suspect Dzhokhar Tsarnaev is detained by officers on Friday, April 19. After a car chase and shootout with police, one suspect in the Boston Marathon bombing, Tamerlan Tsarnaev, was shot and killed by police early Friday, and his brother and second suspect, Dzhokhar Tsarnaev, was taken into custody Friday night. The two men are suspects in the bombings at the Boston Marathon on April 15, that killed three people and wounded at least 170. See all photography related to the Boston bombings.

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Manhunt for Boston bombers – Special imaging techniques employed by Massachusetts State Police reveal Boston Marathon bombing suspect Dzhokhar Tsarnaev hiding in a boat in a backyard in Watertown on April 19.

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Manhunt for Boston bombers – Dzhokhar Tsarnaev gets out of the boat he was hiding in outside of a home in Watertown, as seen in a surveillance video still.

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Manhunt for Boston bombers – An ambulance carries Boston Marathon bombing suspect Dzhokhar Tsarnaev, 19, from the scene after he was apprehended in Watertown, Massachusetts, on April 19.

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Manhunt for Boston bombers – Police SWAT teams leave the area after apprehending the suspect in a yard where he was hiding in a dry-docked boat on April 19.

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Manhunt for Boston bombers – Residents flee from an area where a suspect was hiding on Franklin Street on April 19.

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Manhunt for Boston bombers – SWAT team members run toward a police assault on a house as gunfire erupts on April 19.

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Manhunt for Boston bombers – People react while watching police respond to reported gunfire on April 19.

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Manhunt for Boston bombers – SWAT team members move down residential streets as they perform door-to-door searches in Watertown, Massachusetts, on April 19.

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Manhunt for Boston bombers – A U.S. military helicopter lands behind Watertown Mall as law enforcement agencies continue to search for the 19-year-old bombing suspect on Friday.

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Manhunt for Boston bombers – SWAT teams prepare to enter a home as they continue the door-to-door search.

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Manhunt for Boston bombers – U.S. President Barack Obama meets with members of his national security team in the Situation Room of the White House on April 19 to discuss developments in the Boston bombings investigation.

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Manhunt for Boston bombers – SWAT team members line a residential street in Watertown, Massachusetts, as the manhunt continues on Friday.

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Manhunt for Boston bombers – A man watches from the window of a home as a SWAT team member keeps watch on Friday, in Watertown, Massachusetts.

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Manhunt for Boston bombers – Police to continue to the door-to-door search on Francis Street in Watertown, Massachusetts, on Friday.

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Manhunt for Boston bombers – Law enforcement officers place themselves in an overhead position on Arsenal Street as the search continues on April 19.

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Manhunt for Boston bombers – Law enforcement officers react to what was initially thought to be a threatening suspect on Arsenal Street on April 19.

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Manhunt for Boston bombers – A police SWAT team searches houses on April 19 for the second suspect.

Manhunt for Boston bombers – A Massachusetts state trooper watches other troopers line up at Watertown Mall as the manhunt for the second suspect continues in Watertown on Friday.

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Manhunt for Boston bombers – Police continue the ongoing manhunt for the second suspect on Williow Avenue in Watertown on Friday.

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Manhunt for Boston bombers – A Watertown police vehicle with bullet holes in its body and a shattered windshield is towed out of the search area on April 19 in Watertown, Massachusetts.

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Manhunt for Boston bombers – A Massachusetts State Police officer checks the bag of a cyclist amid heightened security on Friday in Watertown.

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Manhunt for Boston bombers – Katia Costa looks out her window as police continue the manhunt on Nichols Avenue in Watertown on Friday.

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Manhunt for Boston bombers – Ruslan Tsarni, uncle of the Boston terror suspects, told CNN affiliate WBZ that Tamerlan "got what he deserved" in an interview outside his home in Montgomery Village, Maryland, on Friday.

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Manhunt for Boston bombers – A woman is questioned by Cambridge police and other law enforcement agencies Friday near the home of the second suspect in Cambridge, Massachusetts. A Massachusetts Institute of Technology campus police officer was shot and killed late Thursday night at the school's campus in Cambridge. A short time later, police reported exchanging gunfire with alleged carjackers in nearby Watertown.

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Manhunt for Boston bombers – SWAT teams move into position at the intersection of Nichols and Melendy avenues in Watertown, Massachusetts, on Friday.

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Manhunt for Boston bombers – SWAT teams gather at the intersection of Nichols and Melendy avenues in Watertown while searching for the remaining suspect on Friday.

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Manhunt for Boston bombers – Onlookers take pictures while SWAT team members look around on Friday.

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Manhunt for Boston bombers – Massachusetts Gov. Deval Patrick, left, speaks to the media at a shopping mall on the perimeter of a locked-down area during the search on Friday.

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Manhunt for Boston bombers – Metro SWAT members hang off the back of a truck during the search on Friday.

President Barack Obama said the question remained open. "Why did these young men who grew up and studied here as part of our communities and our country resort to such violence? How did they plan and carry out these attacks? And did they receive any help? The families of those killed so senselessly deserve answers," he said Friday.

The question of whether others may have played a role in the blasts could affect the decision by federal authorities not to read Miranda rights to Dzhokar Tsarnaev, who was in serious condition Saturday in a Boston hospital.

The government is invoking the public safety exception, a designation that allows investigators to question Tsarnaev without reading him his Miranda rights, a Justice Department official told CNN on condition of anonymity.

In ordinary cases, suspects are told by police they have the right to remain silent and the right to a lawyer.

But this is no ordinary case, according to U.S. Sens. John McCain of Arizona and Lindsey Graham of South Carolina.

They urged that Tsarnaev be held as an "enemy combatant."

"Now that the suspect is in custody, the last thing we should want is for him to remain silent. It is absolutely vital the suspect be questioned for intelligence gathering purposes," the senators said in a statement. "Under the law of war we can hold this suspect as a potential enemy combatant not entitled to Miranda warnings or the appointment of counsel."

Alan Dershowitz, a prominent defense attorney and Harvard law professor, scoffed at the statement.

"There's no way an American citizen committing a domestic crime in the city of Boston could be tried as an enemy combatant," he told CNN's Piers Morgan. "That shows absolute ignorance of the law."

Dershowitz cited statements made by Boston police as appearing to contradict the government's rationale for invoking the public safety exception.

"The police have said there's no public safety issue. It's solved; it's over," Dershowitz said. "There are no further threats. But the FBI is saying there's enough further threats to justify an exception."

But former New York Mayor Rudy Giuliani said state officials may not be privy to information regarding possible international threats that federal authorities may know about.

"You would have to know the internals of what they have before you can assess whether there is a sensible invocation or not," Giuliani said.

Tamerlan Tsarnaev appears to have become increasingly religious in the last three or four years, according to an analysis of his social media accounts and accounts from family members. But there was no immediate evidence of active association with international jihadist groups.

The only video Tsarnaev posted with a strongly jihadist theme appears to have been reposted on his YouTube page four months ago, about the "emergence of the black flags from the promised land of Khorasan." Khorasan is a reference by jihadis to parts of Afghanistan.

And the devices used in the attacks were rudimentary and could have been built by downloading instructions off the Internet, authorities said.

Still, the investigation is continuing. Whether Tamerlan Tsarnaev's return to Russia in the first half of 2012 changed his outlook is likely to be one of many avenues of inquiry. Before he left, the FBI had already -- at the request of an unidentified foreign government -- investigated possible links with militant groups, but discovered nothing suspicious.

A senior U.S. official told CNN it was Russia in 2011 that asked the FBI to look at Tamerlan Tsarnaev's activities.

The request was based on information that Tamerlan Tsarnaev was a follower of radical Islam, the FBI said.

"I think unless we see some horrible dropping of the ball, I don't think this is an intelligence failure," said former CIA operative Robert Baer. "In retrospect, it might look like one, but I don't think it is."